diff --git a/src/utility-types.ts b/src/utility-types.ts
index 74b604b..21b41c3 100644
--- a/src/utility-types.ts
+++ b/src/utility-types.ts
@@ -13,7 +13,16 @@ import type {
 } from './create-mutation-keys.types';
 import type { AnyMutableOrReadonlyArray } from './types';
 
-type MergeInsertions<T> = T extends object ? { [K in keyof T]: MergeInsertions<T[K]> } : T;
+type Primitive =
+  | boolean
+  | string
+  | number
+  | bigint
+  | symbol
+  | undefined
+  | null
+
+type MergeInsertions<T> = T extends Primitive ? T : T extends object ? { [K in keyof T]: MergeInsertions<T[K]> } : T;
 
 type inferRecordMutationKeys<Target extends object> = {
   [P in Exclude<keyof Target, 'mutationFn'>]: Target[P] extends AnyMutableOrReadonlyArray ? Target[P]